Automotive vehicle engines use various mechanisms and adjustments to vary compression ratio of gasses in the cylinders. Specifically, various approaches are available for adjusting compression ratio during engine and vehicle operation, thereby allowing for improved optimization of fuel economy, emissions, and performance.
The inventors herein have recognized, however, that when transitioning between differing compression ratios during engine operation, such as from low compression to high compression, there may be a disturbance in torque produced by the engine. This disturbance can be such as to be noticed by the vehicle operator, and thereby reduce customer drive feel and satisfaction.
One approach to mitigate torque disturbances in engines has been to utilize adjustment in ignition timing (or spark timing). However, the inventors herein have recognized that spark adjustment authority (or range), may be limited depending on the operating conditions of the engine and vehicle. Therefore, the full compensation of the disturbance may not be achievable in a wide variety of operating conditions. As just one example, ignition timing may be limited by engine knock, or engine misfire limits.